A Three-Tier Architecture with Business Objects

For our final example of what Python can do with data, we’ll look at how Python supports building a three-tier client/server architecture. This will be a fairly straightforward example, as we did a lot of the groundwork in the last section.

Simple database applications have two tiers: database and user interface. A dialog to maintain client details might perform a SELECT query to get all the details of a customer and store those details in the user interface; either directly in text boxes, or in variables stored in the same form or module. When the data has been changed, the system performs an UPDATE query to store the results.

A three-tier architecture creates a Customer class to hold the information, and provides functions to load customers from the database and store them back to it. The GUI layer gets data from the Customer objects. Objects in the middle layer are often known as business objects , because they model things in the business or problem domain, rather than systems objects like database connections, or GUI objects like queries. If you are writing object-oriented programs, you’re already at work on the business objects.

Three-tier also describes network partitioning. With modern distributed-object technologies such as COM and CORBA (and some much lighter alternatives like Python’s RemoteCall package), it’s easy to run the database on one machine, the business objects on another, and the GUI on a third. It’s highly likely ...

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